I cut one of the props down,now it's 11X4,i have put it on and started it but that's all i did,it revved up quicker and seemed to run a lot better.Then i tried a prop that was sent to me,a wood Top Flight Power Point 10X6,wanna know what happened ?i started it and i got a rush of air,the engine was running backwards [X(] ,i killed it and restarted it but the same thing happened,backwards and i know it was running backwards cuz the plane had a very nice reverse. This is gonna open a new can of worms.